1. Field of the Invention
The present invention relates to a method for driving a plasma display panel (PDP).
2. Description of the Prior Art
A method for driving an AC type plasma display panel utilizes wall voltage generated by charge in a dielectric that covers display electrode pairs for a display. Quantity of wall charge in cells to generate display discharge is made larger than quantity of wall charge in other cells in a screen. Binary setting of this wall charge quantity is called addressing. After the addressing, an appropriate sustain pulse (that is also called a display pulse) is applied to all cells simultaneously. By the application of the sustain pulse, drive voltage is added to wall voltage. Display discharge is generated only in cells in which a cell voltage that is the sum of the drive voltage and the wall voltage exceeds a discharge start voltage. Light emission by the display discharge is called “lighting”. By utilizing the wall voltage, it is possible to light only cells to be energized selectively.
In a display of a frame, the addressing is performed at fixed intervals, and initialization is performed in each addressing. The initialization means to clear the binary setting of the wall charge quantity that is kept in the screen at the start time point thereof, namely to equalize wall charge quantity of all cells. When the initialization is finished, the wall charge quantity depends on a form of the addressing. If write form addressing is performed, wall charge quantity of all cells is set to a quantity that cannot generate discharge when the sustain pulse is applied. If an erasing form of addressing is performed, wall charge quantity of all cells is set to a quantity that can generate discharge when the sustain pulse is applied.
As methods for initialization, there are known a method of applying a rectangular waveform pulse having a width smaller than the sustain pulse, a method of applying an obtuse waveform pulse such as a ramp waveform pulse, and a method of applying a rectangular waveform pulse plus an obtuse waveform pulse. These methods generate discharge that is weaker than display discharge and have an advantage that background light emission is little. The background light emission is a phenomenon that a dark portion of an image emits light slightly. In addition, if an obtuse waveform pulse is applied, quantity of the background light emission can be reduced while fine adjustment of the wall charge quantity for compensating variation of the discharge start voltage among cells can be performed. Japanese unexamined patent publication No. 11-352924 describes in detail about the initialization that utilizes “micro discharge” generated by applying an obtuse waveform pulse.
The micro discharge is a very weak discharge responding to the application of an obtuse waveform pulse whose amplitude changes gradually and is distinguished from one-shot discharge responding to the application of a rectangular waveform pulse having sufficient amplitude. The micro discharge starts when the sum of the applied voltage and the wall voltage exceeds the discharge start voltage and lasts until the applied voltage of the obtuse waveform pulse becomes a maximum value (a final voltage) in a continuous manner or a similar intermittent manner.
The conventional driving method has some problems. One is irregularity in a display that becomes conspicuous as time passes from the start of a continuous display that lasts approximately a few hours. Another problem is that the background light emission color becomes not an achromatic color (a dark gray color) but a chromatic color (a reddish, greenish or bluish color) when the initialization by the micro discharge is performed for a color display. Concerning the problem of the background light emission color, Japanese unexamined patent publication No. 2002-278510 discloses a driving method in which amplitude of the obtuse waveform pulse is optimized for each light emission color of a cell. However, this disclosed driving method needs a complicated structure of driving circuit.